Finite Element Analysis Using a Follower Load on Fusion and Non-Fusion Lumbar Spinal Implants

應用伴隨負荷之有限元素模型對融合與非融合腰椎植入物之分析比較

陳世豪(Shih-Hao Chen) ； 江銘傑(Min-Chieh Chiang) ； 鍾政成(Zheng-Cheng Zhong) ； 洪景華(Ching-Hua Hung)

《Journal of Orthopaedic Surgery Taiwan》 26卷4期 (2009/12) Pp. 188-197

並列摘要

Purpose: The follower load tangent to the spinal curvature mimics the physiologic compressive loads for in vivo tests. In vitro tests for spinal implants have advanced from the traditional load-control method (LCM) to the displacement-control method (DCM). This study used a follower load in finite element (FE) models of fusion and non-fusion spinal implants to evaluate the differences of the LCM and DCM at each motion segment.
Methods: A FE model of the intact L1-L5 (INT) was validated and used to implant artificial disc replacement (ADR), or anterior lumbar interbody fusion (ALIF) cage supplement with pedicle screws fixation at the L3-4 level. The follower load was applied by using thermo-isotropic link elements passing through the instantaneous center of rotation at each motion segment with the L5 bottom constrained. The LCM imposed 10 Nm moments of flexion, extension, bending and rotation with a 400 N follower preload. The DCM applied motion that matched the angular displacement noted in the LCM of the INT model. Biomechanical performance of the ADR and ALIF models was compared with the INT model.
Results: At surgical level, the ALIF model had sufficient stability under four physiological motions when using the LCM and DCM. The ADR model maintained the same motion in flexion when using the LCM and DCM, but reduced motions of 20.6%, 8.6% and 9.9% in extension, bending and rotation, respectively, when using the DCM. At adjacent level, the ADR model approached the INT model under all motions (＜10%), when using the LCM and DCM. However, the ALIF model increased motions of 16.6%, 37.7%, 42.5% and 24.7% in flexion, extension, bending and rotation, respectively, when using the DCM, as compared with the LCM.
Conclusions: This study confirmed the applicability of a follower load on the entire lumbar spine under various loading conditions. For the ALIF model, the DCM showed greater motion at adjacent levels than the LCM. For the ADR model, the LCM and DCM revealed similar motions at surgical level; while the DCM had prominent motion variations at adjacent level, as compared with the LCM.

並列關鍵字

load-control method ； displacement-control method ； finite element analysis ； artificial disc replacement ； fusion